Cancer develops when a carcinogen, a substance that causes or aggravates cancer, binds to a cell's DNA and damages it. This results to changes in the cell causing abnormal cell growth. The abnormal cell multiplies and later on forms into a malignant tumor arising within the wall of the lungs or the epithelial lining of the bronchus. There are various causes of lung cancer which include:

1. Smoking is the most important preventable cause. Lung Cancer facts reveal that smoking is one of the leading causes of the disease. A cigarette contains over 60 known carcinogens. A smoker is ten times more likely to develop cancer compared with a non-smoker. The amount, duration, frequency and the tar and nicotine levels in the cigarette correlates to the development of the disease. Secondhand smoke or passive smoke also has a positive relation to this cancer.
2. Environmental and occupational exposure to carcinogens such as asbestos, arsenic, chromates, nickel, radiation, motor vehicle emissions, and other pollutants.
3. Hereditary also plays a factor. There is higher incidence of developing the disease in a person with familial predisposition regardless of his smoking status.

The white area in the upper lobe is cancer; the black areas are discoloration due to smoking

Usually, the patient does not experience any symptoms until the disease is late in its course. Its signs and symptoms are related to the location, size and the degree of the tumor and metastases to other structures.

1. Cough is the most frequent symptom of lung cancer. A cough that starts off as dry and persistent and later on becomes productive should arouse suspicion.
2. Blood-tinged sputum may be expectorated.
3. Wheezing can be noted. It indicates partial obstruction in the bronchus. A wheeze is characterized by a whistling sound over the airways during breathing.
4. Poorly localized chest pain
5. Weight loss, weakness  and fatigue

Prognosis refers to the prediction of the outcome of the disease. There are many factors that influence the prognosis of lung cancer including:

1. Location and size of the tumor
2. Type of  cancer
3. Stage or the degree of spread of the disease
4. Symptoms experienced by the patient
5. Age, response to lung cancer treatment and over-all health status of the patient.